Blow molding a closed plastic drum including two speed compression molding of an integral handling ring

ABSTRACT

A closed one-piece plastic drum having an integral handling ring at a head end is formed in a blow mold having mold halves and an articulating mold section. While the mold is open and the articulating section is spaced from the mold halves, a heated plastic parison is placed in the open mold and blown at a first blowing pressure (30-60 psi) to completely expand the parison into the shape of the inside surface of the mold and fill the open articulating section. This blow molding step forms an open handling ring as well as the drum body. A second blowing operation at a second lower pressure (15-40 psi) is then performed to stabilize the expanded parison inside the mold. The mold articulating section is closed during the second blowing operation in first and second sequences. In each sequence, the articulating section is moved over a different distance and at a different speed while compressing the blow-molded open handling ring into a solid handling ring. After the articulating section is completely closed, a third blowing operation at a third pressure (90-110 psi) is performed. The third pressure is higher than both the first and second pressures and is held for a sufficient time to allow cooling of the molded plastic drum.

This application is a divisional of application Ser. No. 08/312,710,filed Sep. 27, 1994.

FIELD OF THE INVENTION

This invention relates to a one-piece blow-molded closed plastic drumhaving an integrally-formed compression-molded handling ring and methodof molding same which provides a drum construction having structuralstrength and stability to resist breakage of the drum upon impact due totipping or dropping of the drum which would compromise safety in storingand transporting materials including hazardous liquids in such drum.

BACKGROUND OF THE INVENTION

Various liquids, including hazardous liquid materials, are often storedand transported in drums, particularly drums of the 55 gallon type.Drums utilized for transporting of hazardous liquid materials aresubject to rules and regulations of governmental regulatory bodies, suchas the Department of Transportation in the United States. These rulesand regulations require drum constructions to withstand breakage duringdrop and tip tests.

A 55 gallon drum can weigh as much as 880 pounds under acceptableregulations and it is therefore necessary for the manufacturer toprovide the user with some means of moving the drum. The steel drumindustry has developed a device called a "parrot beak" lifting device,which acts like a parrot's beak and squeezes the top chime or handlingring of a drum enough that it will not slip when the drum is liftedusing the device. The device acts by both compressing the handling ringbetween its jaws as well as digging into its surface. Steel drums aremore and more frequently being replaced by plastic drums throughout theindustry for various reasons well known to those in this industry. Thesame parrot beak lifting device is the tool of choice for handling andlifting of filled plastic drums.

Heretofore, there have been several manufacturing methods utilized inproviding plastic drums with a parrot beakable handling ring. One suchmanufacturing method is to shrink-fit a plastic ring onto a blow-moldedplastic drum so tightly that, given the weight placed in the drum, itwill not slip off because the compressive forces on the drum/ringinterface are so large that they overcome the stresses of lifting theassembly via the ring. Other manufacturing methods have includedinjection molding an entire drum head with an integral handling ring andthen sonic welding or hot plate welding such injection molded drum headonto a blow-molded or otherwise formed drum, thus yielding a closed drumwith an integral handling ring for transporting liquid hazardousmaterial. Problems have been presented with both these types of drumsand manufacturing processes from an economic standpoint and from thestandpoint of providing a construction which will satisfactorilywithstand breakage due to forces created during dropping or tipping of afilled drum.

A further preferred manufacturing method for such a plastic drum with ahandling ring would include blow-molding of a drum having a closed headwith an integral handling ring extending therefrom and formed by beingcompression-molded through the use of an articulating section in theblow mold. Such blow-molded drums with compression-molded handling ringshave also suffered from problems relating to breakage of the drum uponimpact during dropping or tipping of a filled drum. The blow-moldingprocessing considerations heretofore utilized have not taken intoaccount stresses caused by such dropping or tipping. Specifically,current designs of drums and their manufacturing processes do notconsider the effects of the flow of plastic material inside the drumduring compression-molding ring formation processes, which createsstress concentrations which limit the usefulness of the drum andresistance to breaking during dropping or tipping. Stress concentrationpoints are created due to the flow of residual materials from thecompression-molding of the integral handling ring unless the directionof flow and the location of the resultant extrudate is carefullycontrolled. Also, current drum designs place the outside surface of thehandling ring outwardly of the outside surface of the drum body whichcauses an inordinate amount of force on the handling ring when a filleddrum is dropped or tipped which causes breakage of the drum particularlyat the stress concentration points.

BACKGROUND AND SUMMARY OF THE INVENTION

It is the object of the present invention to overcome the above problemsheretofore presented with one-piece blow-molded closed plastic drumshaving an integral compression-molded handling ring by providing a drumconstruction and method of manufacturing same which eliminates stressconcentrations heretofore formed in such drums and provides aconstruction which will resist forces on the outside surface of thehandling ring causing breakage of the drum due to impact upon droppingor tipping of a filled drum.

It has been found by this invention that the above object may beaccomplished by providing a one-piece blow-molded closed plastic drumwhich includes a generally cylindrical body portion, a bottomintegrally-molded with a lower end of the body portion and a headportion integrally-molded with an upper end of the body portion anddefining a top and a transition area around and between the upper end ofthe body portion and the top. The drum has a handling ringintegrally-molded with the drum which has a leg extending upwardly fromthe transition area and a grippable member extending generally outwardlyfrom the upper end of the leg and which is parrot beakable.

In accordance with this invention, the transition area preferably has(1) an outside curved surface of a predetermined radius so that anoutside surface of the body portion is positioned in a tangential planein close proximity to a tangential plane along an outer circumferentialsurface of the handling ring and/or (2) an inside curved surface with atleast one radius, preferably defining a double ogee with threepredetermined radii, so that no acute angles are formed between theinside surfaces at the transition area.

With this improved configuration of outside curved surface on thetransition area of the drum, the outside surface of the drum bodyportion will absorb forces of impact on the drum when the drum isdropped or tipped on its side, rather than an inordinate portion of suchforces being directed to the handling ring causing extreme flexingthereof and breaking of the drum in the transition area. On the otherhand, the above-defined improved inside curved surface on the transitionarea of the drum results in no acute angles being formed between insidesurfaces of the drum in the transition area adjacent to the handlingring. It has been found that acute angular formations between insidesurfaces in this transition area caused by the flow of plastic materialduring compression molding of the handling ring result in the formationof stress concentration points in the molded plastic drum which weakenthe drum and cause breakage along such stress concentration points whenforces resulting from dropping or tipping of the drum are exertedthereon.

In order to provide one or both of the above desired improved featuresin the construction of a one-piece blow-molded closed plastic drum withan integral compression-molded handling ring, it has been found that amethod of molding should include the following steps. A blow-mold havingan interior surface of the desired dimensions and shape of the drum tobe molded which includes a cylindrical body portion and a head portionon the end of the body portion and connected thereto by a transitionarea is provided. The mold is designed to form a drum in upside-downposition. Such mold should include an articulating section to blow moldthe head portion and to form by compression a solid handling ringintegrally-extending axially and radially outwardly from the transitionarea of the drum. The interior surface of the mold preferably has ashape to mold a drum having an outside curved surface of a predeterminedradius on the transition area so that the outside cylindrical surface ofthe drum is in a tangential plane in generally close proximity to atangential plane along an outer surface of the handling ring.

A heated plastic parison is provided in the mold. A first blowingoperation of the parison is performed, while the mold articulatingsection is in its open position a predetermined axial distance from theclosed position. The first blowing operation is under a predeterminedpressure to completely expand the parison into the shape of the insidesurface of the mold and to completely fill the open mold articulatingsection and form an open handling ring.

A second blowing operation is performed under a predetermined pressure,less than the predetermined pressure of the first blowing operation, tostabilize the expanded parison inside the mold. The mold articulatingsection is closed, during the second blowing operation, in first andsecond sequences for predetermined different distances of closure atpredetermined different speeds while compressing the blow-molded openhandling ring into a solid handling ring integral with the drum andforming with extruded plastic an inside curved surface on the transitionarea of the drum with at least one radius, preferably in the form of adouble ogee with three predetermined radii, so that no acute angles areformed between inside surfaces of the top, transition area and bodyportion of the drum.

A third blowing operation is then performed after the mold articulatingsection is completely closed at a predetermined pressure higher than thepredetermined pressures of the first and second blowing operations for asufficient length of time to allow cooling of the molded plastic drum.

BRIEF DESCRIPTION OF THE DRAWINGS

While some of the objects, features and advantages of this inventionhave been given above, other objects, features and advantages willappear in the detailed description of preferred embodiments to follow,when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a one-piece blow-molded closed plasticdrum having an integral compression-molded handling ring constructed inaccordance with this invention;

FIG. 2 is an enlarged partial sectional view taken through the drum ofFIG. 1 and along the line 2--2 of FIG.1;

FIG. 3 is a partial sectional view, like FIG. 2, but illustrating theprior art construction of this type of drum and showing the improved newconstruction features in phantom lines;

FIG. 4 is a sectional view through the drum of FIG. 1 and showing suchdrum in position after it has been tipped or dropped onto a flat surfaceand showing force vectors resulting from hydraulic forces produced as aresult of such tipping or dropping of a filled drum onto its side;

FIG. 5 is an enlarged sectional view through the head portion of thedrum and the integrally-molded handling ring extending from a transitionarea between the top of the drum and the body of the drum of FIG. 4 andshowing the effects of dropping or tipping of a filled drum onto a flatsurface;

FIG. 6 is a view, like FIG. 5, but of the prior art drum of FIG. 3 andshowing the effects of dropping or tipping of a filled prior art drumconstruction onto a flat surface which results in breaking of the drumthrough stress concentration points formed in such prior art drum;

FIG. 7 is a sectional, somewhat schematic view illustrating a beginningstep in the manufacturing process of the present invention wherein aheated plastic parison is provided in a blow mold constructed forforming the improved drum of the present invention in upside downposition;

FIG. 8 is a sectional, somewhat schematic view of a next step in formingof the improved drum of this invention wherein a first blowing operationof the parison is being performed;

FIG. 9 is a sectional, somewhat schematic view illustrating a furtherstage of the method of molding a drum in accordance with the presentinvention and wherein the first blowing operation has completelyexpanded the parison into the shape of the inside surface of the moldand has completely filled the open mold articulating section to form anopen handling ring;

FIG. 10 is an enlarged partial sectional view of a bottom portion of themold in the position illustrated in FIG. 9 and at the method stage ofFIG. 9;

FIG. 11 is a further enlarged partial sectional view showing thearticulating section of the mold illustrated in the earlier figures asit begins closing and during a second blowing operation of the parison;

FIGS. 12, 13 and 14 are sectional views which illustrate progressivestages of closing of the articulating section of the mold whilecompression molding the handling ring to a solid handling ring from openhandling ring;

FIG. 15 is a sectional, somewhat schematic view illustrating the moldarticulating head section in its fully closed position and wherein athird blowing operation is being performed; and

FIG. 16 is an enlarged partial sectional view illustrating thearticulating head section in the fully closed position and the resultingcompression molded handling ring with the improved features of theoutside and inside curved surfaces of the transition area between thebody portion and top of the drum.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring now to the drawings, a one-piece blow-molded closed plasticdrum, generally indicated at 10, is illustrated in FIG. 1. This drum 10includes a generally cylindrical body portion 12 defining an outercylindrical surface 12a. A bottom 14 is integrally-molded with a lowerend of the cylindrical body portion 12. A head portion 15 isintegrally-molded with an upper end of the cylindrical body portion 12and defines a top 16 and a transition area 17 around and between theupper end of the body portion 12 and the top 16. A handling ring 20 isintegrally-molded with the drum 10 and has a leg member 21 extendingupwardly from the transition area 17 and a grippable member 22 extendinggenerally outwardly from an upper end of the leg member 21 to define anouter cylindrical surface 22a on the handling ring 22.

The transition area 17 in accordance with this invention preferably hasan outside curved surface 17a of a predetermined radius B so that thebody portion outside surface 12a is positioned in a tangential plane inclose proximity to a tangential plane along the handling ring outsidesurface 22a, as may be seen by the planes indicated schematically at Eand E' in FIG. 2. Said transition area preferably has an inside curvedsurface 17b defining a double ogee with three predetermined radii F, Gand H. For a conventional 55 gallon drum size, it has been determinedthat a predetermined radius B of about 1.0 inch for the outside drumtransition area surface 17a and predetermined radii F, G and H of about0.5 inch, 1.0 inch and 0.5 inch will provide the desired improvements ofthis invention.

The above defined construction of a one-piece blow-molded closed plasticdrum 10 with integrally-molded handling ring 20 may be contrasted withthe more conventional prior art construction of a one-piece blow-moldedclosed plastic drum with an integrally-molded handling ring as shown inFIG. 3. As shown in that figure, the transition area between thecylindrical body portion 12 and the top at the head portion 15 of thedrum 10 has an outside generally flat surface. The handling ring 20 ofthis prior art drum 10, because it extends upwardly and outwardly fromthe transition area, provides an outside surface in a tangential planewhich extends a substantial distance outwardly from a tangential planealong the outside surface of the body portion of the drum, as may beclearly seen in FIG. 3. Also, during the molding method, as will bediscussed in more detail below, the extrudate from compression moldingthe handling ring in the prior art construction results in an insidesurface on the transition area which forms an acute angle N with theinside surface of the top of the drum, thereby producing a stressconcentration at that angle for reasons well understood by those withordinary skill in the art.

Referring now to FIGS. 4 and 5, these figures illustrate the effects ofdropping or tipping a filled drum 10 constructed in accordance with thefeatures described above with respect to FIGS. 1 and 2. FIG. 6illustrates the effects of dropping or tipping a filled drum 10constructed in accordance with the prior art construction discussedabove with respect to FIG. 3.

In FIGS. 4 and 5, a filled drum 10 has been dropped or tipped onto itsside onto a flat surface and the arrows illustrate the force vectorscreated by the hydraulic forces within the filled drum 10. Since theoutside surface 22a is in a tangential plane in close proximity to atangential plane along the outside surface 12a of the body portion 12 ofthe drum 10, minimal forces are exerted by flexing of the handling ring20 when its strikes the surface. Also, stress concentration points inthe transition area 17 of the drum 10 are avoided because of the specialconstruction or geometry in the form of a double ogee of the insidesurface 17b of the transition area 17 of the drum 10. Both of thesefeatures contribute to resisting a breakage of the drum 10 as a resultof tipping or dropping of the drum 10 on its side.

By contrast and referring to FIG. 6, it is shown how the handling ring20 is flexed due to the force of impact against a surface upon droppingor tipping of the filled 10 drum so that these forces cause breakingthrough a break area at a stress concentration in the transition area ofthe drum 10 because of the acute angular relationships of the insidesurfaces of the plastic material in the prior art drum 10.

In order to manufacture a closed one-piece plastic drum 10 having anintegral handling ring 20 having a transition area 17 with the improvedoutside surface 17a and/or inside surface 17b, described above for theimproved resistance to breaking upon tipping or dropping of a filleddrum, a blow-molding method of the following type has been foundsuitable to produce such an improved drum construction. The preferredmethod to be described hereinafter and the preferred mold constructionto be utilized in such method is for construction of a widely used 55gallon type drum. However, it is to be understood that the principals ofthe drum construction and method of this invention are applicable toother size drums and may be easily adapted to other size drums by thosewith ordinary skill in the art.

The preferred method, as disclosed more specifically in FIGS. 7-16includes providing a blow-mold 30 having an interior surface of thedesired dimensions and shape of the drum 10 to be molded, as describedabove with respect to FIGS. 1 and 2, and an articulating mold section 31to blow-mold the head portion 15 of the drum 10 and to form bycompression an integral solid handling ring 20 of the type describedabove with respect to FIGS. 1 and 2. The mold 30 is designed to form thedrum 10 in upside down position. The blow-mold 30 is preferably axiallydivided forming spaced halves 30a, 30b and is initially positioned in anopen position.

A heated plastic parison 33 is provided in the mold 30, preferably byextruding such heated plastic parison between the open mold halves 30a,30b, as shown in FIG. 7. Extruding of a plastic parison, which isinitially longer than the drum to be blow-molded, is an operation wellunderstood by those with ordinary skill in the art and does not needfurther detailed explanation herein. The plastic parison 33 may beconstructed of any thermoplastic material, including but not limited topolyolefins, styrenics, PET, PVC, polycarbonate, ABS, nylonpolyphenylenes, polyacetals, polyesters which demonstrates adequaterheological properties which lend themselves to blow molding, andcombinations thereof. The parison 33 is preferably heated toapproximately 412 degrees F.

The method further includes performing a first blowing operation of theparison 33 by blow pins 35 extending into the parison through thearticulating section 31 of the mold 30 in a manner well understood bythose with ordinary skill in the art. This first blowing operation ofthe parison 33 is performed while the articulating section 31 is in anopen position a predetermined axial distance of at least 2.65 inchesfrom a closed position, as illustrated in FIGS. 7, 8 and 9. This firstblowing operation is performed while closing the blow-mold halves 30a,30b from the position of FIG. 7 to that of FIG. 8 and under apredetermined pressure of about 30-60 PSI to completely expand theparison 33 into the shape of the inside surface of the mold 30 and tocompletely fill the open mold articulating section 31 and form an openor hollow handling ring 20, as shown in FIGS. 9 and 10.

The minimum open distance of 2.65 inches for the articulating section 31is important to ensure that enough plastic material from the parison 33can be expanded into this open articulating mold section 31 tocompletely fill the handling ring mold surfaces therein, leavingsufficient plastic material to extrude back into the inside surface ofthe transition area 17 of the drum 10 to form the double ogee curvedinside surface 17b as the mold articulating section 31 closes tocompression-mold a solid handling ring 20 on the drum 10.

As the parison 33 is extruded into the mold 30 in its open position, itis programmed to adjust the wall thickness to ensure the presence ofsufficient plastic material. Once the parison 33 is extruded to thecorrect length, the first blowing operation is commenced and the moldhalves 30a, 30b close to pinch off the parison from the extruding deviceand provide a closed parison within the mold 30. This first blowingoperation is continued until the mold halves are completely closed.

The next step in the method is a second blowing operation on theexpanded parison 33 which is conducted under a predetermined pressure,less than the predetermined pressure of the first blowing operation, atabout 15-50 psi to stabilize the expanded parison 33 inside the closedmold 33. During this second blowing operation, the mold articulatingsection 31 is closed in first and second sequences for predetermineddifferent distances and at predetermined different speeds whilecompressing the blow-molded open handling ring 20 into a solid handlingring 20 integral with the drum 10 and forming with extruded plastic aninside curved surface 17b on the transition area 17 of the drum 10 inthe form of a double ogee with three predetermined radii F, G, H.

Prior to activating closing of the mold articulating section 31, a twosecond delay is provided following complete closure of the mold halves30a, 30b to give sufficient time to completely expand the parison 33into the articulating mold section 31 prior to beginning closurethereof. The second blowing operation under the above described pressurestabilizes the parison 33 within the mold 30 as the articulating section31 is closing.

Failure to use the low pressure of between about 15 to 40 PSI and usinga higher pressure of about 50 to 110 PSI can cause several problems tooccur. Firstly, the plastic material stretched into the openarticulating mold section 31 can rupture, leaving voids in the handlingring 20 or not forming the handling ring 20 at all. Secondly, due tohigh pressure in the mold 30, compounded with the contraction of thearticulating mold section 31 being closed, the air pressure can becometoo great and cause the mold 30 to open up to relieve the built-up airpressure, leaving a blown-out pinch off area generally on the bottomsection of the drum 10.

Closing of the mold articulating section 31 in first and secondsequences for predetermined different distances and at predetermineddifferent speeds, along with the shape of the mold surface to provide anoutside curved surface 17a having a predetermined radius B at thetransition area 17 of the drum 10, causes the flow of the plasticextrudate on the inside of the drum 10 at the transition area 17 duringcompression molding of the handling ring 20 to assume the curved insidesurface 17b in the shape of a double ogee having three predeterminedradii F, G, H.

During the first sequence of closing of the mold articulating section31, the mold is closed approximately 70 percent at a predetermined speedof approximately 1.85 inches per second for a period of 1 second traveltime. This initial movement is used in order to quickly gather the blownplastic material in the open handling ring channel filling the outeroverhang on the handling ring 20 (see FIG. 11 which shows thearticulating head section closed by a distance of 3/4 inch). Next, aslower speed of approximately 10-11 percent of the speed of closingduring the first sequence is utilized to continue the process ofcompressing the open handing ring into a solid handling ring 20 andextruding the material to flow out to achieve the desired inside surface17b geometry on the transition area 17 of the drum 10.

FIGS. 12, 13, 14 and 15 show the stages of compression molding the openhandling ring 20 into a solid handling ring 20 integral with the drum 10while forming with extruded plastic the inside curved surface 17b on thetransition area 17 of the drum 10 in the form of the double ogee withthree predetermined radii F, G, H. These views show the articulatingmold section 31 stopped at 5 millimeter increments in sequence to betterillustrate the actual movement of the plastic material. FIG. 12 shows across-section of the handling ring 20 with the articulating mold section31 about 0.59 inches from being completely closed. At this time thearticulating mold section 31 is closing in its second sequence at theslower speed. It should be noted that the outer lip of the handling ring20 is basically formed and filled from faster movement of the moldsection 31 in the first sequence. As the articulating mold head sectioncloses to approximately 0.394 inches from closing, as shown in FIG. 13,the handling ring 20 has joined and a sharp angle is being formed at theintersection of the inside wall surface of the top 16 and the insidewall surface of the transition area 17. In FIG. 14, the articulatingmold section 31 is 0.197 inches from full closure and the handling ring20 is completely filled and free of voids and the angle between theinside wall of the transition area 17 and the top 16 is a virtual 90degree angle. Finally, during the last and final closure of thearticulating mold head section 31 to form the inside surface 17b of thetransition area 17 in the double ogee shape, as illustrated in FIG. 16,sufficient material is left to be extruded out to form this desiredinner geometry free of all acute angles and stress concentration pointsassociated with them. This double ogee curved inside surface 17b on thetransition area 17 provides strength and flexibility in this criticalsection of the drum 10 to resist fracture during dropped or tippedimpact.

The molding method concludes with a third blowing operation after themold articulating section 31 is completely closed at a predeterminedpressure higher than the predetermined pressures of the first and secondblowing operation of about 90-110 PSI for a sufficient period of time toallow cooling of the molded plastic drum 10. Following cooling, the moldhalves 30a, 30b may be opened up along with the mold articulatingsection 31 and the molded drum 10 removed from the mold 30.

Thus, this invention has provided an improved one-piece blow-moldedclosed plastic drum 10 having an integrally-formed compression-moldedhandling ring 20 wherein a transition area 17 around and between theupper end of a cylindrical body portion 12 and the top 16 of the drum 10has an outside curved surface 17a of a predetermined radius B so that anoutside surface 12a of the body portion 12 is positioned in a tangentialplane E in close proximity to a tangential plane E' along an outercircumferential surface 22a of the handling ring 20 and/or thetransition area 17 has an inside curved surface 17b defining a doubleogee with three predetermined radii F, G, H so that no acute angles areformed between inside surfaces.

With this construction, the outside surface 12a of the drum body portion12 will absorb forces of impact on the drum 10 when the drum 10 isdropped or tipped, rather than an inordinate portion of such forcesbeing directed to the handling ring 20 causing a breaking of the drum 10in the transition area 17. Also, the improved inside curved surface 17bon the transition area 17 of the drum results in no acute angles beingformed between inside surfaces of the drum 10 in the transition area 17adjacent to the handling ring 20 avoiding the formation of stressconcentration points in the molded plastic drum 10 which weaken the drumand cause breakage along such stress points when forces resulting fromdropping or tipping of the drum 10 are exerted thereon.

The improved molding method for this drum construction 10 includes stepswhich ensure the flow of plastic material in an extrudate along theinside surface 17b of the transition area 17 from an open blow-moldedhandling ring 20 as the open blow-molded handling ring 20 iscompression-molded into a solid handling ring 20 due to methodconditions during the compression molding and due to the shape of thedrum being molded so that the extrudate will form the improved insidecurved surface 17b on the drum.

The invention has been described in considerable detail with respect toits preferred embodiments. However, variations and modifications can bemade within the spirit and scope of the invention as described in theforegoing specification and as defined in the following claims.

What is claimed is:
 1. Method of molding a closed one-piece plastic drumhaving an integral handling ring at a head end thereof and comprisingthe steps of:providing a blow mold having an interior surface of thedesired dimensions and shape of the drum to be molded which includes acylindrical body portion and a head portion including a top on one endof the body portion and connected thereto by a transition area, andhaving an articulating mold section to form by compression a solidhandling ring integrally extending axially and radially outward from thetransition area of the drum; providing a heated plastic parison in themold; performing a first blowing operation of the parison, while themold articulating head section is in open position a predetermined axialdistance from a closed position, under predetermined pressure tocompletely expand the parison into the shape of the inside surface ofthe mold and to completely fill the open articulating section and forman open handling ring; performing a second blowing operation underpredetermined pressure, less than the predetermined pressure of thefirst blowing operation, to stabilize the expanded parison inside themold; closing the mold articulating section, during the second blowingoperation, in first and second sequences for predetermined differentdistances at predetermined different speeds while compressing theblow-molded open handling ring into a solid handling ring integral withthe drum and forming with extruded plastic an inside curved surface onthe transition area of the drum with at least one radius so that noacute angles are formed between inside surfaces of the top, transitionarea and body portion; and performing a third blowing operation afterthe mold articulating section is completely closed at a predeterminedpressure higher than the predetermined pressures of the first and secondblowing operations for a sufficient time to allow cooling of the moldedplastic drum.
 2. Method, as set forth in claim 1, wherein said step ofclosing the articulating mold section further includes forming withextruded plastic material the inside curved surface on the transitionarea of the drum in the form of a double ogee with three predeterminedradii.
 3. Method, as set forth in claim 1, wherein the step of providinga blow mold having an interior surface of the desired dimensions andshape of the drum further includes providing a portion of the moldinterior surface in a shape to mold a drum having an outside curvedsurface of a predetermined radius on the transition area so that theoutside cylindrical surface of the drum is in a tangential plane ingenerally close proximity to a tangential plane along an outer surfaceof the handling ring.
 4. A method, as set forth in claim 1 or 3, whereinsaid step of performing a first blowing operation is performed at apredetermined pressure of approximately 30-60 PSI.
 5. A method, as setforth in claim 1 or 3, wherein said step of performing a second blowingoperation is performed at a predetermined pressure of approximately15-40 PSI.
 6. A method, as set forth in claim 1 or 3, wherein said stepof performing a third blowing operation is performed at a predeterminedpressure of approximately 90-110 PSI.
 7. A method, as set forth in claim1 or 3, wherein said step of performing a first blowing operation isperformed at a predetermined pressure of approximately 30-60 PSI, andwherein said step of performing a second blowing operation is performedat a predetermined pressure of approximately 15-40 PSI, and wherein saidstep of performing a third blowing operation is performed at apredetermined pressure of approximately 90-110 PSI.
 8. Method, as setforth in claim 1 or 3, wherein said step of providing a blow moldfurther includes providing a axially divided blow mold forming spacedhalves in an open position, wherein said step of providing a heatedplastic parison includes extruding a plastic parison between the openblow mold halves, and wherein said step of performing a first blowingoperation of the parison includes closing the blow mold halves duringsaid first blowing operation.
 9. Method, as set forth in claim 8,wherein said step of performing a first blowing operation of the parisoncontinues for about 2 seconds after the mold halves are closed to ensurethat the parison is completely expanded inside the mold and completelyfills the open articulating section.
 10. Method, as set forth in claim 1or 3, wherein said step of closing the mold articulating sectionincludes closing said articulating section a predetermined distance ofat least approximately 2.65 inches.
 11. Method, as set forth in claim10, wherein said step of closing the mold articulating section in firstand second sequences further comprises closing the articulating sectionapproximately 70 percent during the first sequence at a predeterminedspeed and closing the articulating section the remaining 30 percentduring the second sequence at a slower speed of approximately 10 percentof the speed of closing during the first sequence.
 12. A method ofmolding a closed one-piece 55 gallon plastic drum having an integralhandling ring at a head end thereof and comprising the stepsof:providing an axially divided blow mold forming space halves in anopen position and having an interior surface of the desired dimensionsand shape of the drum to be molded which includes a cylindrical bodyportion and a head portion on one end of the body portion and connectedthereto by a transition area, and having an articulating section to formby compression a solid handling ring integrally extending axially andradially outward from the transition area of the drum, the mold beingfurther shaped to provide an outside curved surface of a predeterminedradius on the transition area of the drum so that the outsidecylindrical surface of the drum is in a tangential plane in closeproximity to a tangential plane along an outer surface of the handlingring; extruding a heated plastic parison between the open blow moldhalves; performing a first blowing operation of the parison, whileclosing the blow mold halves and while maintaining the mold articulatingsection in open position a predetermined axial distance of at leastapproximately 2.65 inches from a closed position, under a predeterminedpressure of 30-60 PSI to completely expand the parison into the shape ofthe inside surface of the mold and to completely fill the open moldarticulating section and form an open handling ring, the firstblow-molding operation continuing for about 2 seconds after the moldhalves are closed to ensure that the parison is completely expandedinside the mold and completely fills the open articulating sectionduring the first blow-molding operation; performing a second blowingoperation under a predetermined pressure of 15-40 PSI to stabilize theexpanded parison inside the closed mold; closing the mold articulatingsection during the second blowing operation in a first sequence in whichthe mold is closed approximately 70 percent at a predetermined speed andin a second sequence in which the mold is closed the remaining 30percent at a predetermined slower speed of approximately 10 percent ofthe speed of closing during the first sequence while compressing theblow-molded open handling ring into a solid handling ring integral withthe drum and forming with extruded plastic an inside curved surface onthe transition area of the drum in the form of a double ogee with 3predetermined radii; and performing a third blowing operation after themold articulating head section is completely closed at a predeterminedpressure of 90-110 PSI for a sufficient time to allow cooling of themolded plastic drum.
 13. Method, as set forth in claim 12, wherein thespeed of closing of the mold articulating head section during the firstsequence is approximately 1.85 inches per second and during the secondsequence is approximately 0.20 inch per second.